1. Field of the Invention (Technical Field)
The present invention relates to methods and devices for electrosurgery, including devices that operate in a conductive media, including an aqueous conductive media, by means of oxygen and hydrogen combustion.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
A variety of electrosurgical devices, used for cutting, ablation, and the like in surgical procedures, are known. In general, it is claimed that these devices utilize mechanisms of action based on various plasma formation physiochemical paradigms. A plasma, broadly defined as “the fourth state of matter” as opposed to solids, liquids, and gases, is a state in which atoms have been broken down to form free electrons and stripped nuclei by the application of high energy or temperatures (ca. 106 degrees). In a plasma, the charge of the electrons is balanced by the charge of the positive ions so that the system as a whole is electrically neutral. The energy input required to initiate a plasma is related to the initial state of the matter as a solid, liquid, or gas, the molecular bond energy, and the ease with which electrons can be stripped from their orbits, among other variables. The percent of the samples that actually become a plasma is usually very small due to the large energy requirements to create a plasma (i.e. ˜0.1% of a mole). Further, a plasma can be constrained by magnetic fields lowering the input energy necessary. A sustainable plasma often requires a vacuum or magnetic field control since the plasma elements quickly seek to be grounded, quenching the plasma; however, some systems may form short duration plasmas on the order of nano- or micro-seconds depending upon energy input and degree of vacuum/magnetic field present.
Some prior art references disclose electrosurgical devices with claimed use of a gas plasma consisting of an ionized gas that is capable of conducting electrical energy. In certain of these devices, either ambient air or a supplied gas is used for ionization, such as the devices disclosed in U.S. Pat. Nos. 5,669,904, 6,206,878 and 6,213,999. If a gas is supplied, it is an inert gas such as argon. In general, these devices are intended for use in ambient atmosphere for the treatment of soft tissue.
Other electrosurgical devices function in liquid media and utilize some form of radiofrequency (RF) energy, such as with two or more electrodes. Heat is generated by use of the RF energy, resulting in destruction or ablation of tissues in proximity to the electrodes. Thus the devices may be employed for coagulation of blood vessels, tissue dissection, tissue removal, and the like. U.S. Pat. No. 6,135,998 teaches an electrosurgical probe immersed in liquid media or tissue, wherein an electrical pulse is applied, with the claimed result that “plasma streamers” are formed from the endface area of a first electrode. In this patent, it is claimed that cutting action results from the plasma streamers. The minimum voltage is on the order of 1.5-2.0 kV, with 15 kV being the preferred maximum voltage, at a minimum power dissipation of 500 Watts, and preferable a higher power dissipation of 800 to 1500 Watts.
Other lower energy electrosurgical devices are known, consisting of monopolar and bipolar configurations that function at energy configurations at or below 1.4 kV and 300 Watts. Both monopolar electrosurgical devices, in which the electrosurgical device includes an active electrode with a return electrode separately connected to the patient such that direct electric current flows through the patient's body, and bipolar electrosurgical devices, in which the electrosurgical device includes both active and return electrodes, are now well known in the art. These electrosurgical device configurations can be used in ambient air or in a fluid medium. In general, it has been believed that these electrosurgical devices generally operate by means of creation of a plasma or some related form of ionization. Thus prior art devices, such as that disclosed in U.S. Pat. No. 5,683,366, are claimed to rely on the fluid irrigant components participating in ionic excitation and relaxation, with attendant release of photonic energy. This mode of operation is often referred to as “utilizing a plasma”. Prior art methods claiming an ionized vapor layer or plasma include, in addition to the patents disclosed above, the methods disclosed in U.S. Pat. Nos. 5,697,882, 6,149,620, 6,241,723, 6,264,652 and 6,322,549, among others.
A plasma requires that atoms be completely ionized to a gas of positive ions and electrons, and, if sustainable, would likely need to occur in a vacuum-like environment. It is unlikely that many, if not most, prior art devices generate a plasma even for a short time. This most notably follows from consideration of the overall energy balance required to initiate or sustain a plasma in either ambient air or aqueous, cellular, or other biologic environments. The nominal 200 to 1500 Watts of power normally employed in a typical electrosurgical device, or any other energy level or configuration contemplated for electrosurgical application (most, however, are between 200 and 300 Watts), is insufficient to initiate and/or sustain a plasma, even in a vacuum and with magnetic field control, even for a short period of time. For example, in a saline solution typically utilized during electrosurgery, 49.6 kW-s/mole (I eV=5.1390; II eV=47.2864; III eV=71.6200; etc.) is needed to ionize sodium, while the ionization energy of simple water is 12.6206 eV (i.e. one electron volt=1.602177×10−19 Joules) as referenced in CRC Handbook of Chemistry and Physics, 72 ed., Lide, David R., CRC Press, 1991. The energy to initiate a plasma typically exceeds the ionization potential of a material, and to sustain a plasma requires an even greater energy input. Further, once ions have been formed in solution, such as in an aqueous solution of sodium as employed in electrosurgery, a yet even greater energy input is required.
Further, many prior art electrosurgical references ignore recognized phenomena relating to plasmas, such as the large ionization potentials and energy necessary to initiate a plasma or to sustain a plasma and the role of the vacuum or magnetic fields in such circumstances. Most electrosurgical devices cannot deliver the energy required to initiate, let alone sustain, a plasma; and, further, electrosurgical applications do not occur in a vacuum environment or in a magnetically controlled environment. The energy needed to create a plasma in vivo during electrosurgery would overwhelm the ability of the host organism to withstand such an energy insult globally. Plasma cutters as used in metal fabrication are examples of the high energy necessary to “utilize a plasma” at normal pressures; yet such high energy levels certainly have not been contemplated for electrosurgical application due to the significant iatrogenic damage that would occur. This understanding has led us to search for other physiochemical paradigms to understand electrosurgery as it is practiced at energy configurations amenable and safe for in vivo application and to more fully and correctly explain common physiochemical observations during electrosurgery in order to create more appropriate electrosurgical devices and methods.
In industrial settings, it is known to employ an oxygen and hydrogen combustion reaction, such that a “water torch” results by ignition of co-mingled oxygen and hydrogen gas molecules liberated from water through high frequency electrolysis, as is disclosed in U.S. Pat. No. 4,014,777. However, such methods have never been intentionally applied to medical procedures, such as for electrosurgical devices and methods. Further, such devices and methods have never been optimized for the constraints of use of electrosurgical devices on biologic tissue, including constraints resulting from the presence of discrete quantities of electrolyte fluids, the presence of physiologic fluids and materials, the desires to minimize collateral tissue injury, the need to avoid generation of toxic by-products, the attendant host organism tissue response, and the like.
There is thus a need for electrosurgical devices that are optimized to the true physical and chemical processes involved in the operation and use of such electrosurgical devices upon biologic tissue within this energy spectrum and power range.